| Acronym | Meaning |
| LEPD | Low-Energy Positron Diffraction |
| LEPECVD | Low Energy Plasma Enhanced Chemical Vapor Deposition |
| LEPS | London-Eyring-Polanyi-Sato (potential-energy Surface) |
| LEPS+IDI | London-Eyring-Polanyi-Sato + Ion Dipole Induced [potential] |
| LERAM | Littoral Ecosystem Risk Assessment Model |
| LERPC | Ligand-exchange Reagent Performance Check |
| LERS | Low-energy Recoil Scattering |
| LET | Light-emitting Transistor |
| LET | Linear Energy Transfer (in Spacecraft Power Systems) |
| LEU | Low Enrichment Uranium |
| LEV | Low Emission Vehicle |
| LFA | Long-chain Fatty Acid(s) |
| LFAM | Line Focus Acoustic Microscope |
| LFC | Load Frequency Control (battery Systems) |
| LFC | Loss-free Counting |
| LFC | Lowest Feasible Concentration |
| LFCC | Laboratory-frame Close-coupling (for Electron-mol. Scattering) |
| LFECA | Low Frequency Eddy Current Array |
| LFER | Linear Free Energy Relationship |
| LFG | Landfill Gas |
| LFHO | Linearly Forced Harmonic Oscillator |
| LFL | Lower Flammable Limit |
| LFM | Lateral Force Microscopy |
| LFMO | Ligand Field Method Combined With Linear Combination Of Atomic Orbitals-molecular Orbital Method |
| LFRT | Long Fiber Reinforced Thermoplastic |
| LFS | Li-Fraumeni Syndrome |
| LFT | Liver Function Test |
| LGFSTF | Liquefied Gaseous Fuels Spill Test Facility (DOE Mercury |
| LGIC | Ligand-gated Ion Channel |
| LGL | Large Granular Lymphocyte |
| LGM | Last Glacial Maximum (most Recent Era Of Continental Glaciation; See Also PGP) |
| LGM | Linearized Green-function Method (for Electronic-structure) |
| LGO | Light Gas Oil |
| LH | Luteinizing Hormone |
| LHASA | Logic And Heuristics Applied To Synthetic Analysis |
| LHC | Large Hadron Collider |
| LHD | Lower Hybrid Drift |
| LHDAC | Laser Heated Diamond Anvil Cell |
| LHDC | Lube Hydrocracking Distillate Catalyst |
| LHEA | Laboratory For High Energy Astrophysics |
| LHM | Longuet-Higgins-Murrell Approximation |
| LHON | Leber's Hereditary Optic Neuropathy |
| LHP-RHF | Longuet-Higgins-Pople Restricted Hartree-Fock Method |
| LHPG | Laser-heated Pedestal Growth |
| LHRH | Luteinizing Hormone-releasing Hormone |
| LHS | Latin Hypercubic Sampling |
| LHSF | Local Hyperspherical Surface Functions (in Quantum Calcns. On Reactive Scattering) |
| LHSV | Liquid Hourly Space Velocity |
| LIBD | Laser-induced Breakdown Detection |
| LIBORS | Laser Ionization Based On Resonance Saturation |